Accurate partitioning mechanisms ensure the propagation of organelles through subsequent generations. They may also help determine the developmental fate of different daughters. Errors might not only lead to developmental defects but also tumorigenesis. Though the mechanisms underlying chromosomal segregation are well advanced, much less is known about the partitioning of other cellular organelles. This is particularly true for membrane-bound organelles, especially the Golgi apparatus, the focus of this application. Two models have been put forward to explain the partitioning of this organelle. The first argues that the Golgi membranes themselves mediate partitioning, fragmenting at the onset of mitosis, and reassembling in each daughter cell during telophase. The second model argues that the endoplasmic reticulum mediates partitioning, the Golgi merging with it during mitosis and emerging once partitioning of the endoplasmic reticulum is complete. Our data continue to favor the first model but there are unresolved differences between workers concerning the mechanism of Golgi enzyme partitioning. In an effort to resolve these differences and to provide more insight into Golgi partitioning, we shall introduce several new microscopic techniques that will provide a higher resolution view of this process. In addition, one of these techniques involves biotinylation of golgin-84, a new member of the golgin family of Golgi structural proteins that we think is involved in Golgi biogenesis and partitioning. Golgin-84 was discovered as the binding partner of a synaptojanin homologue implicated in oculocerebrorenal syndrome. Since other golgin family members were identified as antigens in the auto-immune disease, Sjogren's syndrome, the hope is that studying these Golgi structural proteins will also shed light on these syndromes.